This invention relates to a gas insulated switch-gear, more particularly it is concerned with improvement of a gas insulated switch-gear apparatus being housed in a switching house.
The voltage of power electric line is being stepped up with the increase in electric power demand, and a power electric line with a voltage ranging from 500 to 800 KV has been realized.
Accordingly, a power electric sub-station or power electric switching station provided on a power electric line with such an ultra-high voltage requires a large installation area. For example, in the case of the line voltage being 500 KV, an insulation distance between the respective three phases or insulation distance from the ground amounts to 8 meters including some allowance. Therefore, it is advantageous that the switch-gear used is formed into a gas insulated switch-gear wherein power circuit breakers, disconnecting swtiches, earthing switches and the like provided in a power electric sub-station or power electric switching station are enclosed in earthed metallic vessels and insulation therein is effected by means of SF6 gas with a high dielectric strength and excellent arc-suppressing characteristics.
According to the arrangement of gas insulated switch-gear described above, it is possible to reduce the installation area of the components into about one tenth thereof and render the switching apparatus compact in size. While, the insulation distance between a bus bar and a feeding bus bar, both of which are electrically connected to the switching apparatus, cannot be decreased. Moreover, a multitude of insulators insulatingly supporting the respective bus bars should be large and long on account of securing the insulation distance against the support frame of bus bars.
Furthermore, the respective bus bars are provided outdoors and hence, if the aforesaid station is located adjacent to sea shore, the station is liable to be affected by salty wind and also by sand and dust. For this reason, frequent maintenance services are required and reliability tends to be lowered.
Therefore, it is desirable to install said bus bars, gas insulated switching apparatus and further current transformers, voltage detectors, spark gap devices and the like in the switching house.
When these components are installed in the switching house, a wall bushing should be mounted in the side wall of the switching house in order to connect these components to the power electric line.
In the case of the power electric line of 500 KV class, the length of said wall bushing from its support portion to its terminal portion comes up to about 8 meters at the outdoor side, it comes up to about 6 meters at the indoor side. Accordingly, the weight of it amounts to several tons and hence the side wall of the switching house should be firmly reinforced. Moreover, such bushings are needed at opposite sides of the switching house, whereby the weight comes up to be doubled so that the construction cost is greatly increased. Furthermore, since the wall bushings are projectingly provided within the switching house, the switching house is reduced in its space factor, thereby necessitating the switching house to be constructed large in size. Additionally, said wall bushings are normally formed into oil filled condenser type bushings and hence, when said bushings are horizontally, penetratingly provided through the walls of the switching house, insulation oil feed means should be mounted at a position fairly high over the ground level, thereby causing difficulties in maintenance services.